1. Field of the Invention
The present invention relates to an angular velocity sensor preferably used to sense the angular velocity of, for example, a rotary member and the like.
2. Description of the Related Art
An angular velocity sensor of prior art will be described based on FIG. 16 to FIG. 18.
In the drawings, numeral 1 denotes an angular velocity sensor made by a micromachining technology and numeral 2 denotes a substrate formed of, for example, a monocrystal silicon material of high resistance so as to constitute the main body of the angular velocity sensor 1 and the substrate 2 is formed to a rectangular sheet-shape as shown in FIG. 16 and FIG. 17. For convenience, the direction perpendicular to the lengthwise direction of the substrate 2 is called an X-axis direction and the thickness direction thereof is called a Z-axis direction here.
Numeral 3 denotes a movable portion composed of polysilicon of low resistance with which impurities such as P, B, Sb etc. are doped. The movable portion 3 is formed on the substrate 2 through an insulation film 4 (see FIG. 18) composed of, for example, silicon oxide or the like and formed on the surface of the substrate 2. The movable portion 3 is composed of a pair of support portions 5 fixed so as to define in a Y-axis direction, four support beams 6 having base ends formed integrally with the respective support portions and linearly extending in the Y-axis direction and an approximately rectangular oscillator 7 formed to the extreme ends of the respective support beams 6 integrally therewith. Movable-side comb-shaped electrodes 8, 8 composed of a plurality of electrode plates 8A are projectingly formed to both the right and left side surfaces of the oscillator 7 in the X-axis direction. Further, the movable portion 3 is arranged such that only the respective support portions 5 are fixed to the substrate 2 and the respective support beams 6 and the oscillator 7 are held in parallel with the substrate 2 in the state that they are spaced apart therefrom a predetermined distance so that the oscillator 7 can be displaced in the X-axis direction and the Z-axis direction with respect to the substrate 2.
Numerals 9, 9 denote fixed-side comb-shaped electrodes disposed on the substrate 2 so as to be located on the right and left sides of the oscillator 7. The respective fixed-side comb-shaped electrodes 9 are composed of fixed portions 9A, 9A located on both the right and left sides of the oscillator 7 and disposed on the substrate 2 and a plurality of electrode plates 9B projectingly formed to the respective fixed portions 9A so as to confront the respective electrode plates 8A of the movable-side comb-shaped electrodes 8. Then, as shown in FIG. 17, the movable-side comb-shaped electrode 8 confronts the fixed-side comb-shaped electrode 9 through an interval and the respective electrode plates 8A and the respective electrode plates 9B are alternately disposed so that they are meshed with each other.
Numerals 10, 10 denote oscillation generators serving as oscillation generation means and each of them is composed of the movable-side comb-shaped electrode 8 and the fixed-side comb-shaped electrode 9. When an oscillation drive signal of a frequency f is alternately imposed on the respective oscillation generators 10, an electrostatic attracting force is generated between the respective electrode plates 8A, 9B in an opposite direction alternately and the oscillator 7 is oscillated in the X-axis direction by the electrostatic attracting force as shown by an arrow A.
Numeral 11 denotes a substrate side electrode formed on the substrate 2. As shown in FIG. 18, the substrate side electrode 11 is formed to have conductivity by being densely doped with impurities such as, for example, P, Sb etc. on the surface thereof, and is located below the oscillator 7 and confronts the oscillator 7 such that it is spaced apart therefrom a predetermined distance.
Numeral 12 denotes a displacement sensing unit serving as displacement sensing means which is composed of the oscillator 7 and the substrate side electrode 11 and senses the change in interval between the oscillator 7 and the substrate side electrode 11 in the Z-axis direction as a change in capacitance therebetween.
In the angular velocity sensor 1 arranged as described above, when the oscillation drive signal of a frequency f acting as an opposite phase is imposed on the respective oscillation generators 10, the oscillator 7 is oscillated in the x-axis direction with respect to the substrate 2 as shown by the arrow A of FIG. 16 and when an angular velocity .OMEGA. is imposed on the substrate 2 in this state using the Y-axis as a rotating axis, a Coriolis force (inertia) F is alternately generated in the Z-axis direction to the oscillator 7 in proportion to the angular velocity .OMEGA..
As a result, the oscillator 7 is oscillated in the Z-axis direction with an amplitude proportional to the Coriolis force F and the angular velocity .OMEGA. imposed about the Y-axis is sensed by sensing the change in amplitude (displacement) of the oscillation as the change in capacitance between the oscillator 7 and the substrate side electrode 11 by the displacement sensing unit 12.
Further, since the Coriolis force F acting on the oscillator 7 is also proportional to the magnitude of the amplitude resulting from the oscillation in the direction of the arrow A which is generated in the X-axis direction, the angular velocity sensor 1 can sense the angular velocity .OMEGA. about the Y-axis with a pinpoint accuracy by making the frequency f of the oscillation drive signal to be imposed approximately equal to the dynamic resonant frequency of the oscillator 7 so as to increase the displacement of the oscillator 7 in the Z-axis direction caused by the Coriolis force F by greatly oscillating the oscillator 7 in the X-axis direction.
Incidentally, in the aforesaid prior art, the angular velocity sensor 1 is arranged to sense an angular velocity about only one axis such as, for example, the Y-axis. At present, however, a sensing accuracy is enhanced by sensing angular velocities about two axes perpendicular to each other in such applications as the prevention of oscillation caused by hand in video cameras, the sensing of angles in car navigation, and the like, thus there are employed two angular velocity sensors each sensing an angular velocity about one axis with the sensing axes of these angular velocity sensors being disposed perpendicular to each other.
Therefore, in the aforesaid angular velocity sensor 1, it is contemplated to dispose the two angular velocity sensors 1 so that the sensing axes thereof are perpendicular to each other to sense angular velocities about two axes perpendicular to each other. In such an arrangement, however, there is a problem that it is very difficult to dispose the axes with a pinpoint accuracy and yield is lowered in manufacture. Also, since a space in which the angular velocity sensors 1 are mounted to a printed circuit board is needed, the size of video camera sets and the like is increased. Further, although it is also contemplated to form the two angular velocity sensors 1 on the substrate 2 so that the sensing axes thereof are perpendicular to each other, there is a problem that the area of the substrate 2 is increased and the miniaturization of the angular velocity sensor 1 is made difficult as well as a manufacturing cost is increased.
Further, since the resonant frequency of the oscillator 7 has a certain degree of dispersion, when the oscillators 7 of the above respective angular velocity sensors 1 have a different resonant frequency, an oscillation drive signal generating circuit is necessary for each of the angular velocity sensors 1, by which the substrate area of the generating circuits is increased.